DISTRIBUTION AND RICHNESS OF RARE TREE SPECIES IN ARAUCARIA FOREST FRAGMENTS, ALONG AN ALTITUDINAL GRADIENT, IN SANTA CATARINA STATE, BRAZIL

The present study aimed to analyze how the distribution and the richness of rare tree species occur along an altitudinal gradient, in Araucaria Forests fragments. For this purpose, tree species (diameter at breast height >= 5 cm) were sampled in 10 forest fragments located on different altitudinal floors in "Planalto Sul-Catarinense" region, totaling 10 ha of sampling area. The species with only one or two individuals in at least one fragment were classified as rare. The species distribution was verified by a dendrogram constructed through the Jaccard floristic distance index and the UPGMA clustering algorithm. The total species richness per fragment and the number of rare species were compared among montane and upper-montane sub-formation by the Mann-Whitney (U) test. The relationship between altitude and values of total richness and number of rare species in each fragment were determined by simple linear regressions. The results indicated the formation of two groups of rare species, in function of the altitude floor. Despite the fact that total richness of communities decreased with increasing altitude, the number of rare tree species did not significantly change. We conclude that in the "Planalto Sul-Catarinense" region, the fragments of Araucaria Forest have different set of rare tree species according to altitude and that the reduction of the richness of communities with increasing altitudinal floor is not accompanied by a reduction in the number of rare species.